Direct current (DC) systems are widely used in various fields such as automatic transmission systems, DC micro-networks, and marine systems. In these fields, the DC system usually provides a voltage to multiple loads coupled in parallel. However, an overcurrent fault which may be caused by a short circuit condition, for example, could introduce a cascaded failure to the loads due to the large current in DC bus bars, DC capacitors, and power converters. Overcurrent fault protection is thus one critical challenge for the DC system. Usually a protection system is provided for detecting fault conditions and operating one or more protection devices to isolate the fault area.
Mechanical breakers and fuses are conventionally used in fault protection systems. These components are designed to remove power from an electrical device when an unbearable high current flowing through the electrical device is detected. Opening or tripping a mechanical breaker, however, is not instantaneous and may generate an arc. A fuse is dependent upon an overheating condition which usually lags behind the overcurrent fault and must be replaced each time it is tripped. Some known types of protection systems are configured to allow the fault current to conduct for up to several tens of milliseconds, which may cause a cascaded failure of the electrical device.
Another more recently developed type of protection system is based on a high power semiconductor device such as an integrated gate commutated thyristor (IGCT). Due to the nature of the semiconductor device, the trip time required for isolating the overcurrent fault which may be caused by a short circuit fault may be shortened to several tens of microseconds. However, limiting the fault current flowing through the semiconductor device to a controllable value for repeatable use of the protection system is a challenge.
Therefore, it is desirable to provide systems and methods to address the above-mentioned problems.